Ent-draughts

Though little is known about them in detail, they seem to have been made from river-water, but with unique and subtle flavours reflecting the Ents' association with trees and forests. The first time Merry and Pippin imbibed an ent-draught it reminded them of the smell of a distant wood brought from afar by a cool night breeze. The second time they drank the flavour was earthier and richer, more food-like.[1]

Their power of growth was most evident when they were drunk by beings other than Ents: the Ent-draughts taken by Merry and Pippin added three inches or more to their heights,[2] making them the tallest Hobbits in the history of the Shire.[3]